The freshman congressman voted against the bill when it passed the House in November by the narrow margin of 220 to 215. Mr. Massa was one of 39 Democrats to vote no.

He said he favored a single-payer healthcare system, and felt the House bill did not go far enough to bring down healthcare costs. Massa’s departure will eliminate one of the “no” votes that House Speaker Nancy Pelosi needs to overcome as she seeks support to pass the Senate version of reform.

Massa is leaving Congress sooner than he had originally planned – at 5 p.m. on Monday, his office confirmed Friday.

On Wednesday, he had announced he would leave the House when his term ends, citing health problems. But the House ethics committee has confirmed that it was investigating Massa. It has been widely reported that he allegedly sexually harassed a male staff member, a charge Massa denies.

The bad news for Democrats is twofold: One of their members is embroiled in an embarrassing scandal (though getting Massa out of the House sooner rather than later is a plus). And his seat is vulnerable to a GOP takeover, as the district leans right and the seat was long held by Republicans.

The question is, when will Massa be replaced? Under state law, Gov. David Paterson (D) – another troubled New York politician – must declare the seat vacant and then set a date for a special election.

But there’s no deadline for declaring the seat vacant, so it’s possible it will not be filled until the November election.